Such motors are for example described in FR-2 754 953. Thus, reference is made in particular to a polyphase motor consisting, on the one hand, of a fixed part or stator, energized by electric coils and, on the other hand, a magnetized mobile part or rotor. The latter includes N1 pairs of poles radially magnetized in alternate directions, N1 being equal to 4 or 5. As to the stator, it includes N2 identical poles, N2 being equal to 9 so that these poles are spaced apart by 40°. Besides, they are assembled consecutively 3 by 3 so that each phase consist of a W-shaped circuit, grouping three consecutive stator poles. The central pole of the W bears the winding of said phase. Besides, the central poles of two W-shaped circuits are angularly spaced apart by 120°.
These elements are arranged in a common stage, that is substantially in the game plane, in order to optimize costs and size of the parts they are comprised of, such as the magnets.
For this type of motor, it is usual to detect the displacement of the mobile rotor part in the magnetic circuit. In fact, this rotor part induces a flow variation, a variation that can be detected by an electromagnetic type position sensor.
Therefore, such actuators are capable of providing a representative image of the position of the load energized directly or, more frequently, through a reducing gear, thanks to a position control, therefore requiring an appropriate electronic control device and a position sensor for the mobile organ. This sensor is, in most cases, of the potentiometric, magnetic, or optic type, and it is mounted on the back of the actuator.
Naturally, this position sensor requires, for this reason, an extra space at the level of the actuator, not to mention that some of its constituent elements have to be extended in order to permit this detection of the rotation of the mobile organ. In this context, moreover, one has to make sure that the presence of these sensors does not influence the propagation of the magnetic flows between different the stator poles.
Furthermore, in such a construction, the electric connection of this or these sensors and that of the actuator to the electronic control card turns out to be relatively complex.